During all the service life, bridge structure subjected to environmental attack and repeatedly loads, which leads deformation wider, more surface carbonization and steel embedded corrosion seriously. Two corrosion models are introduced in this paper, the random variables are determined, the failure probability is calculated by Monte-Carlo method. The reliability factors, such as material variation, dead loads, live loads, corrosion rate are analyzed also. It shows the decreasing rate of cross section area is faster than that of local corrosion’s, the failure probability is bigger too. The effective cross-section area of steel-bar, yield strength, and live loads is more sensitive on failure probability.